1. Technical Field
This invention relates to a switching element control apparatus for controlling a switching element that is driven by controlling a voltage on its control terminal.
2. Related Art
One of known switching element control apparatuses for controlling a switching element that is driven by controlling a voltage on its control terminal is a gate drive circuit disclosed in Japanese Patent Application Publication No. 2009-071956.
The gate drive circuit disclosed in Japanese Patent Application Publication No. 2009-071956 is adapted to drive a power switching element. The disclosed gate drive circuit includes a first turn-on side power supply circuit and a second turn-on side power supply circuit. The first turn-on side power supply circuit includes a first turn-on voltage source and a first switch. The second turn-on side power supply circuit includes a second turn-on voltage source, a second switch, and a turn-on side delay circuit. A first turn-on voltage of the first turn-on voltage source is set lower than a second turn-on voltage of the second turn-on voltage source.
When a command signal for turning on the power switching element is inputted to the gate drive circuit, the first switch is turned on and the first turn-on voltage of the first turn-on voltage source is applied to a gate of the power switching element. The command signal is delayed by the turn-on side delay circuit. When the command signal delayed by the turn-on side delay circuit is inputted to the second switch, the second switch is turned on and the second turn-on voltage of the second turn-on voltage source is applied to the gate of the power switching element. That is, the first turn-on voltage lower than the second turn-on voltage is applied to the gate of the power switching element during turn-on operation of the power switching element, and then when the power switching element transitions to a steady state, the second turn-on voltage is applied to the power switching element.
Keeping the gate voltage at a low level during turn-on operation of the power switching element can suppress a collector current following through the power switching element. This can prevent breakage due to a surge voltage and breakage due to heat generation even when the power switching element is turned off in the presence of an abnormality, which can increase a tolerance of the power switching element to breakage. Raising the gate voltage upon transition to the steady state can reduce steady state losses of the power switching element.
However, since the disclosed gate drive circuit includes two power supplies having mutually different voltages, the gate drive circuit has a more complicated circuit configuration.
In addition, since switching characteristics are varied with power switching elements, a delay time of the turn-on side delay circuit, the first turn-on voltage of the first turn-on voltage source, and the second turn-on voltage of the second turn-on voltage source have to be set in response to the characteristics so that the power switching element can be controlled properly. However, the delay time, the first turn-on voltage, and the second turn-on voltage are set by hardware, which makes their settings unable to be changed in response to the characteristics of the power switching element. This prevents the power switching element from being controlled properly in response to its characteristics.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing a simply constructed switching element control apparatus capable of controlling a switching element properly in response to its characteristics.